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Chapter 20: Q11CQ (page 731)
If aluminium and copper wires of the same length have the same
resistance, which has the larger diameter? Why?
As aluminum鈥檚 resistivity is higher than copper's, and resistivity is related to the
cross-sectional area, the aluminum wire has a bigger diameter.
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(a) Redo Exercise\({\rm{20}}{\rm{.25}}\)taking into account the thermal expansion of the tungsten filament. You may assume a thermal expansion coefficient of\({\text{12}} \times {\text{1}}{{\text{0}}^{{\text{ - 6}}}}{\text{ / C}}\).
(b) By what percentage does your answer differ from that in the example?
(a) Find the voltage drop in an extension cord having a \({\bf{0}}{\bf{.0600}}\;{\bf{\Omega }}\) resistance and through which \({\bf{5}}{\bf{.00}}\;{\bf{A}}\) is flowing. (b) A cheaper cord utilizes thinner wire and has a resistance of \({\bf{0}}{\bf{.300}}\;{\bf{\Omega }}\). What is the voltage drop in it when \({\bf{5}}{\bf{.00}}\;{\bf{A}}\) flows? (c) Why is the voltage to whatever appliance is being used reduced by this amount? What is the effect on the appliance?
Explain the properties of myelinated nerves in terms of the insulating properties of myelin.
Find the power dissipated in each of these extension cords:
(a) an extension cord having a \(0.0600\;\Omega \) resistance and through which 5.00A is flowing;
(b) a cheaper cord utilizing thinner wire and with a resistance of \(0.300\;\Omega \).
Using an ohmmeter, a student measures the resistance between various points on his body. He finds that the resistance between two points on the same finger is about the same as the resistance between two points on opposite hands鈥攂oth are several hundred thousand ohms. Furthermore, the resistance decreases when more skin is brought into contact with the probes of the ohmmeter. Finally, there is a dramatic drop in resistance (to a few thousand ohms) when the skin is wet. Explain these observations and their implications regarding skin and the internal resistance of the human body.
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